Various paths interfere with wireless communication signals which are transmitted through a channel. The interference causes signal fading and signal attenuation which lowers a signal to noise ratio (SNR) as a result, thereby deteriorating a quality of a received signal.
Therefore, methods which receive the received signals through several antennas (for example, an array antenna) in order to reduce interference of a signal in accordance with multiple paths have been suggested. The multiple antenna has an excellent effect to improve a quality of the signal, but since individual antennas are configured by active antennas, the number of RF transceivers is undesirably increased in proportion to the number of antennas.
In order to solve the above-mentioned problem, a beam forming antenna using a single RF transceiver has been suggested. The beam forming antenna drives an active antenna through a single RF chain and adjusts a reactance of a parasitic antenna to adjust a direction of the beam, thereby increasing reception sensitivity. However, a single RF chain beam forming antenna of the related art has the following problems.
First, complex channel modeling and a digital process are required to achieve beam forming to increase the reception sensitivity. The method has a long computing time, so that it is difficult to track a signal source which varies in real time and a load for a digital block is increased. Therefore, it is difficult to maximize an effect of reducing the RF chain.
Second, since it is required to complete beam tracking during an idle time to change a beam pattern of an antenna, the computing time is increased as the number of parasitic antennas is increased, so that it is difficult to exactly estimate a direction of the beam. Further, since the RF chain cannot receive the signal while finding the beam, the reception efficiency is reduced. Specifically, in spite of detecting an optimal direction, there may be an additional problem in that the sensitivity of the signal is ironically reduced during a computation period to track the other direction.
Third, a reactance load to form a pattern of a beam generally uses a capacitance between both ends of a variable diode element or a phase shift technology of a parasitic antenna using a phase shifter, but in order to implement a desired capacitance, the variable diode needs to be applied with high power voltage of 10 V or larger and the minute adjustment of the phase shifter is not possible for each, and an insertion loss is large, so that it is difficult to apply the antenna of the related art to the system.